GStreamer —— 2.2、Windows下Qt加载GStreamer库后运行 - “教程2:GStreamer 概念“（附：完整源码）

运行效果

简介

上一个教程演示了如何自动构建管道。现在我们将通过实例化每个元素来手动构建管道并将它们全部链接在一起。在此过程中，我们将学习：

• 什么是 GStreamer 元素以及如何创建一个。

• 如何将元素相互连接。

• 如何自定义元素的行为。

• 如何观察总线的错误条件并提取信息来自 GStreamer 消息。

这些元素是 GStreamer 的基本构造块。他们处理数据从源元素（数据生产者）流向下游传递给 sink 元素（数据使用者），通过 filter 元素。

GStreamer相关运行库

cpp 复制代码

INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include/gstreamer-1.0/gst
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include/gstreamer-1.0
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include/glib-2.0
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/lib/glib-2.0/include

LIBS += D:/Software/GStreamer/1.0/mingw_x86_64/lib/gstreamer-1.0.lib
LIBS += D:/Software/GStreamer/1.0/mingw_x86_64/lib/glib-2.0.lib
LIBS += D:/Software/GStreamer/1.0/mingw_x86_64/lib/gobject-2.0.lib

完整源码

cpp 复制代码

#include <QCoreApplication>
#include <QDebug>

#include "gst.h"

int tutorial_main()
{
    GstBus *bus;
    GstMessage *msg;
    GstStateChangeReturn ret;

    /* 初始化GStreamer */
    gst_init (nullptr,nullptr);

    /* 创建元素 */
    GstElement *source = gst_element_factory_make ("videotestsrc", "source");       // 元素输出
    GstElement *sink = gst_element_factory_make ("autovideosink", "sink");          // 元素输入

    /* 创建空管道 */
    GstElement *pipeline = gst_pipeline_new ("test-pipeline");
    if (!pipeline || !source || !sink) {g_printerr ("Not all elements could be created.\n");return -1;}

    /* 构建管道 */
    gst_bin_add_many (GST_BIN (pipeline), source, sink, NULL);
    if (gst_element_link (source, sink) != TRUE)
    {
        g_printerr ("无法链接元素.\n");
        gst_object_unref (pipeline); return -1;
    }

    /* 修改元素的属性 */
    g_object_set (source, "pattern", 1, NULL);

    /* 开始播放 */
    ret = gst_element_set_state (pipeline, GST_STATE_PLAYING);
    if (ret == GST_STATE_CHANGE_FAILURE)
    {
        g_printerr ("无法将管道设置为播放状态.\n");
        gst_object_unref (pipeline); return -1;
    }

     /* 用于获取与特定元素相关联的消息总线(message bus)函数。
     * 消息总线是用于在管道的不同部分之间传递消息的机制，例如错误、警告、EOS（End Of Stream）事件等。 */
    bus = gst_element_get_bus (pipeline);
    /* 等待错误或流结束,获取并解析消息 */
    msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE, (GstMessageType)(GST_MESSAGE_ERROR | GST_MESSAGE_EOS));
    if (msg != NULL)
    {
        GError *err;
        gchar *debug_info;

        switch (GST_MESSAGE_TYPE (msg))
        {
        case GST_MESSAGE_ERROR:
            gst_message_parse_error (msg, &err, &debug_info);
            g_printerr ("从元素接收到错误 %s: %s\n", GST_OBJECT_NAME (msg->src), err->message);
            g_printerr ("调试信息: %s\n", debug_info ? debug_info : "none");
            g_clear_error (&err);
            g_free (debug_info);
            break;
        case GST_MESSAGE_EOS: g_print ("流已结束.\n"); break;
        default:
            /* 不应该到达这里，因为我们只要求错误和EOS */
            g_printerr ("收到意外消息.\n"); break;
        }
        gst_message_unref (msg);
    }

    /* 释放资源 */
    gst_object_unref (bus);
    gst_element_set_state (pipeline, GST_STATE_NULL);
    gst_object_unref (pipeline);
    return 0;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

#if 1
    tutorial_main();
#else
    gst_init(nullptr,nullptr);

    const gchar *nano_str;
    guint major,minor, micro,nano;
    gst_version(&major, &minor, &micro,&nano);

    qDebug() << major << " " << minor << " " << micro << " " << nano;
#endif

    return a.exec();
}

关注

笔者 - jxd